Progress on two of three, and insight to problems with the third.
I installed an AM and a narrow CW (250Hz B/W; 8.9MHz CF) filter in one of the queued-up '980s today and used that radio to test my repairs to the various PLL/VCO Units I have on hand. It still has some warm-up drift which I think will be cured with a master reference oscillator crystal swap. FWIW, Yaesu was still stocking these as of a few years ago (thanks Jose!) but I'm going to look into modifying one of my spare BFO Units to use a garden variety 30.0000MHz computer timebase crystal.
After the RX sections were working, I turned to Ye Olde Junque Box and retrieved one of what is probably the last unused Gen TX kits in existence. It went into the first of the rigs, though it looks like a TX parameter-set procedure is in order. Good power below 14MHz; not so much above. There's adjustments for that.? I had another Gen TX kit on what now appears to be a defunct RF Unit; it was bought for parts regardless and after I removed the kit the board was cycled back into the spares collection. That kit was put in radio #2, which also needs a bit of alignment. Part of this evening was spent setting IF stage gains and getting S meters to accurately track the generator output.
The deaf-as-a-post repair mule got a little more bench attention. It faintly hears a .01uV signal but the AGC doesn't appear to be very effective between On and Off, and I cannot adjust the S meter. Thoughts are that the AGC Detector/Amp section is wonky. Of course, this discovery was made after I bought another IF Unit from the action site...but spares are nice to have, I suppose.
That rig also suffer from the same tuning problem as another rig (still in line) does, and which I detailed in a thread earlier this year. I think what's going on is the MC14093B on the Dial Unit, which receives pulses from the photointerruptors and conditions them. CMOS of the period occasionally goes bad from "tin whiskers". I have another Dial Unit to swap into Radio #3 (due to come out of line when the ones I'm working on go back in service) and have a bunch on 14093Bs inbound too.
One of our members posted an ALC mod which shortens the response. I think both of the rigs currently on the bench sorely need it, based on observations of how the rig controls TX power. There appears to be a positive feedback loop in place due to the long action time - this causes a power rise. One more thing to investigate.
Have a few more mods up my sleeve once everything is up and running. Chief among these are auxiliary cooling fans.
73 - Fred, N8YX
